1. Field of the Invention
The present invention relates to an electrostatic actuator, an electrostatic actuator driving method, an electromechanical transducer, a waveform output device, and the electromechanical transducer and an electric element in which the waveform output device is incorporated, particularly to those in which high-accuracy control can be performed while power consumption can be reduced.
2. Description of the Related Art
The electrostatic actuator which generates electrostatic force between a stator and movable element constituting the actuator to drive the movable element by repulsion/attraction of the electrostatic force, is well known (see Jpn. Pat. Appln. KOKAI Publication No. 8-140367 and Jpn. Pat. Appln. KOKAI Publication No. 10-239578). As shown in FIG. 39, the electrostatic actuator includes an MPU (waveform data generation unit) 2001, a waveform output register 2002, an output waveform generation unit 2003, a switching circuit 2004, and an actuator (stator and movable element) 2005. FIG. 40 shows a process of inputting data to the waveform output register 2002 on the basis of a control program stored in a program ROM 2006.
In the electrostatic actuator, as shown in FIG. 41, a current position and a drive direction of the actuator (the current position and the drive direction of a movable element relative to a stator) are calculated by combining a control program and the MPU 2001 (ST1). An appropriate waveform data (drive time and drive pattern) is extracted from a waveform data string on the program ROM 2006 to set the waveform data in the waveform output register 2002 (ST2). The output waveform generation unit 2003 generates the waveform data on the basis of the waveform data set in the waveform output register 2002. The switching circuit 2004 converts the waveform data into voltage and the voltage is applied to electrodes provided in the actuator (movable element and stator).
It is decided whether the predetermined drive time has elapsed or not (ST3). When the predetermined drive time has elapsed, in accordance with the current position and drive direction of the actuator, the appropriate waveform data is set into the waveform output register 2002 from the waveform time data string in order to output the next waveform data.
In addition to the electrostatic actuator, the electromechanical transducer such as a piezoelectric actuator is known as the device in which drive force is generated by applying the voltage (Jpn. Pat. Appln. KOKAI Publication No. 2001-119917 and Jpn. Pat. Appln. KOKAI Publication No. 2002-27767).
The following problem exists in the electrostatic actuator and the electrostatic actuator driving method. Namely, in order to correctly generate the waveform data to a set minimum waveform unit time (for example, 0.1 ms to 1 ms), it is necessary to suppress the step of calculating the current position and the drive direction of the movable element to a sufficiently small value (for example, not more than 1/1000) relative to required resolution (0.1 ms) of the drive waveform. In order to realize the requirement, it is necessary to drive the MPU at extremely high speed. For example, when about 3000 clocks are necessary to calculate the current position and drive direction of the movable element, the clock of 300 MHz is required for the MPU. In such high-speed clock, power consumption is increased in the MPU, and the high-speed clock is not appropriate to mobile applications in which there is little margin in the power source.
There is known the control unit which controls actuators such as the electrostatic actuator, the piezoelectric actuator, and a stepping motor and electronic devices such as LED using the waveform signal. FIG. 42 shows an example of the control devices. FIG. 42 shows a configuration of a general purpose processor having a parallel output port (for example, see Jpn. Pat. Appln. KOKAI Publication No. H6-277894). An MPU 2010 performs processing by reading a command set of a program RAM 2011. The MPU 2010 writes the data in an output data register 2012 if necessary, and the MPU 2010 transmits the data to an output waveform generation unit 2013. The output waveform generation unit 2013 transmits the waveform signal to a switching circuit (not shown) to drive the actuator or the like. The MPU 2010 has a timer inside MPU 2010 to perform time management. When the MPU having the parallel output port is used, the control device can be easily formed because the MPU 2010 can perform the time management by itself.
FIG. 43 shows another example of the control devices. FIG. 43 shows the configuration of the control circuit of the stepping motor (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2000-94569). A control unit 2020 decides a drive direction (CW/CCW) bit for determining a rotation direction of the stepper, and the control unit 2020 also decides whether a stepping motor 2023 is operated in a half step or a full step. The control unit 2020 outputs a half step mode (HSM) bit and a STEP bit in which one step provides a direction of the generation at each negative edge of a STEP signal. A waveform data generation unit 2021 generates a specific sequence from the three bits and outputs the sequence to ports PA1 to PB2. The waveform data generation unit 2021 prepares four types of drive patterns, and the waveform data generation unit 2021 has a function of controlling which sequence is invoked depending on the state of a flag. A switching circuit 2022 receives the output data (TTL level, e.g. 3.3V) of the waveform data generation unit 2021 to output current (for example, 500 mA) having a voltage level (for example, 10V) necessary to drive the stepping motor 2023. There are many digital still camera lens actuator using the stepping motor controller.
The following problem exists in the control device which outputs the waveform signal. Namely, when the processing device (MPU) simultaneously performs time management and waveform management, it is necessary that the MPU should be driven at high speed in order to perform the time management with high accuracy. Specifically, in order to correctly generate the drive pattern to the set minimum waveform unit time (for example, 0.1 ms to 1 ms), it is necessary to suppress the step of calculating the current position and the drive direction of the movable element to the sufficiently small value (for example, not more than 1/1000) relative to required resolution (0.1 ms) of the drive waveform.
Accordingly, when about 3000 clocks are necessary to calculate the current position and drive direction of the movable element, the clock of 300 MHz is required for the MPU. When such high-speed clock is used, the power consumption is increased in the MPU. As a result, there is the problem that the high-speed clock is not appropriate to mobile applications in which there is little margin in the power source. Since, usually, the system clock is of the order of 10 MHZ, it is difficult to correctly perform the time management by the above-described configuration.
Since periodic ON/OFF signal having a plurality of different phases is used in the stepping motor controller, several types of output waveform patterns are previously determined. On the other hand, in the general purpose actuator (electrostatic actuator), the huge number of drive patterns can be generated depending on the form of the actuator (auto-focusing, zooming, and other applications). Therefore, since the configuration of the controller significantly depends on the form of the actuator, it is difficult that all the drive sequences are previously installed in the controller. Since the general purpose actuator is not compatible with the drive sequence which is not previously assumed, there is the problem that the drive sequence of the general purpose actuator is not compatible when the configuration of hardware (the number of input terminals) of the actuator is changed after a chip has been developed.